A through hole is formed in order to obtain electric conductivity of a top and a bottom of a printed wiring board. As an example thereof, a penetration opening is formed through a double-sided copper plated laminate board by means of a drill, an electric conductor layer is formed at the opening by means of plating or the like, and etching is applied as necessary, thereby forming a circuit. In this manner, a printed wiring board having an electric conductor circuit and enabling electric conductivity of a top and a bottom is formed. These wiring boards are prepared in plurality, and then, a further multi-layered printed wiring board is obtained via a prepreg. Alternatively, while a wiring board having a through hole is used as a core, an inter-layered insulation layer and an electric conductor layer are formed to obtain a multi-layered printed wiring board.
In recent years, with a growing demand for high density of a printed wiring board, reducing an drilling diameter of a through hole more remarkably has been discussed.
In order to manufacture a printed wiring board along the above growing demand, there is a need for a small diameter drill for opening a small diameter through hole. Such a small diameter drill is disclosed in Utility Model JP 7-33514 A or JP 2004-82318 A and the like.
According to JP 2004-82318 A, rigidity is enhanced, and good hole precision is obtained by using a drill having formed thereon a shaving discharge groove formed in one stripe, the drill having 5/100 or less in diameter with respect to the maximum outer diameter of a blade tip portion.